The invention relates to a device and a process for processing a signal comprising determining means to supply an output signal having a value representative of a time constant of a part of an input signal having an appreciably exponential form. The invention also relates to an electrical apparatus comprising at least one electrical conductor and at least one temperature sensor with fluorescent or luminescent material arranged near to said electrical conductor.
Known processing devices designed to give a value representative of a signal of exponential form generally use a sampling system to evaluate the signal at several points. The values of the measured samples then enable the amplitude and the time constant of the signal on the descent to be determined. However, when the signal contains noise or disturbances, such a measuring method does not enable precise values of the input signal to be obtained.
When the input signal is supplied by a sensor with fluorescent or luminescent material, the form of the signal is appreciably exponential on the descent and of small amplitude. Thus, as the signal is weak, disturbances are liable to be superposed on the signal. If amplifiers are used to amplify the signal, these disturbances persist and an offset signal can be added to the amplified signal. Such degradations make precise measurement of certain characteristics of the signal difficult, in particular extraction of a quantity representative of a time constant of exponential form.
The object of the invention is to achieve a device and a process for processing a signal enabling precise measurement of a quantity representative of a time constant of appreciably exponential form of a signal and an apparatus comprising such a device.
In a device according to the invention, the determining means comprise:
first integrating means to supply a first integration signal representative of integration of the input signal in a first direction during a first preset time and of integration of the input signal in a second direction opposite to the first direction during a second preset time succeeding the first time and of appreciably equal value to said first time, and
extraction means connected to the first integrating means to supply, as a function of the first integration signal, the output signal having the value representative of a time constant of a part of a signal having an appreciably exponential form.
In a preferred embodiment, the determining means comprise second integrating means to supply a second integration signal representative of integration of the input signal in a first direction during a third preset time different from the first time and starting appreciably at the same time, and of integration of the input signal in a second direction opposite to the first direction during a fourth preset time succeeding the third time and of appreciably equal value to said third time, the extraction means being connected to the first integrating means and to the second integrating means to supply said output signal as a function of the first integration signal and the second integration signal.
Preferably, the first integration signal and/or the second integration signal are determined by at least one integration time of a reference signal between at least one of the values of the first and/or second of the integration signals after integration during a second time or a fourth time and a reference value triggering an end of integration.
Advantageously, the extraction means comprise means for determining the ratio between the first integration signal and the second integration signal, the value of the output signal being determined as a function of said ratio.
Preferably, the extraction means comprise a table of values to assign values of the output signal according to the ratio between the first integration signal and the second integration signal.
Preferably, the determining means comprise switching means to switch at least one input of the integrating means between an input signal and an inverted input signal, and a reference signal.
In a particular embodiment, the device comprises amplifying means to receive a measurement signal and to supply the input signal to the determining means.
In a particular embodiment, the device comprises means for receiving a light signal connected to the amplifying means, the light signal being supplied by a sensor with fluorescent or luminescent material.
For example, the light signal supplied by a sensor with fluorescent or luminescent material can be a signal representative of a temperature.
An electrical apparatus according to the invention, comprising at least one electrical conductor and at least one temperature sensor with fluorescent or luminescent material arranged near to said electrical conductor, comprises a processing device as defined above connected to said temperature sensor.
Preferably, a part of said at least one electrical conductor is in the form of an electric shunt and the fluorescent or luminescent material of the sensor is arranged on the part of the conductor in the form of an electric shunt.
In a particular embodiment, the electrical apparatus comprises:
at least one electrical contact in series with said at least one electrical conductor, and
means for processing tripping functions connected on output of the processing device to receive the output signal having a value representative of a time constant, and connected to a trip relay to command opening of said contacts.
In a preferred embodiment, said apparatus is an electrical circuit breaker.
In a signal processing process according to the invention comprising a determining phase to supply a value representative of a time constant of a part of an input signal having an appreciably exponential form,
the determining phase comprises:
a first step of integration of the input signal in a first direction during a first preset time,
a second step of integration of the input signal in a second direction opposite from the first direction during a second preset time appreciably equal to the first time and succeeding said first step, and
an extraction step to supply the value representative of a time constant as a function of the signal integrated by the first and second integration step.
Preferably, the determining phase comprises:
a third step of integration of the input signal in a first direction during a third preset time different from the first time and starting appreciably at the same time as said first step,
a fourth step of integration of the input signal in a second direction opposite from the first direction during a fourth preset time appreciably equal to the third time and succeeding said third step,
the extraction step supplying the value representative of a time constant as a function of the signal integrated by the first and second integration step and of the signal integrated by the third and fourth integration step.
Advantageously, the extraction step supplies the value representative of a time constant as a function of the ratio between the signal integrated by the first and second integration step and the signal integrated by the third and fourth integration step.